Ticks are obligate blood-feeders and temporary ectoparasites of terrestrial vertebrates. Among arthropods, ticks are second only to mosquitoes in transmitting pathogens to humans, pets, livestock, and wild animals. Certain species of the genus Dermacentor are the most important tick-vectors from both the medical and veterinary perspectives;for example, they are vectors of Rickettsia rickettsii causing Rocky Mountain spotted fever;Rickettsia sibirica causing North Asian tick typhus;Rickettsia conori causing Boutenneuse fever;Francisella tularensis causing tularemia in humans;and pathogens causing anaplasmosis, babesioses, and theileriosis in animals. These species also transmit several viruses that cause human diseases. In North America, the bites of some species of Dermacentor can result in paralysis in humans and domestic animals. Correct identification of tick species, particularly in the immature stages, is essential for epidemiology, prevention, and treatment of tick-borne diseases. However, identifying Dermacentor species is challenging because we have no comprehensive work on their systematics;identifying the nymphal and larval stages is almost impossible due to the lack of taxonomic work. The overall objective of the proposed project is to develop a global-scale, comprehensive, and effective tool for identification of Dermacentor species, including their immature stages. This objective will be achieved through four specific aims: Aim 1. To produce a global-scale taxonomic revision of the genus Dermacentor;Aim 2. To produce tools to identify the immature stages of Dermacentor integrating all possible evidence;Aim 3. To develop a DNA barcode system for Dermacentor species;and Aim 4. To reconstruct a phylogeny for Dermacentor species using mitochondrial and nuclear genes. Impact. Identification of tick species is the first and essential step of study and management of tick- borne diseases. Conducted research on systematics of the Dermacentor ticks will allow better understanding of their ecology and geographic distribution which in turn will help in establishing and improving adequate methods of control these tick-vectors. Investigation of the evolutionary history of these ticks will help us to understand the evolution of vector competence and provide a strong basis for establishing a meaningful classification system. Our investigation will be the first of its kind and is fundamental to fulfilling our long-term goals, which are to produce comprehensive identification tools for all tick species of the family Ixodidae. PUBLIC HEALTH RELEVANCE: Ticks in the genus Dermacentor are important vectors of the organisms causing Rocky Mountain spotted fever (Rickettsia rickettsii), North Asian tick typhus (Rickettsia sibirica), Boutenneuse fever (Rickettsia conori), tularemia (Francisella tularensis), Omsk hemorrhagic fever, Colorado tick fever, and Crimean-Congo hemorrhagic fever in humans. Identifying tick species correctly is an essential task for the study of tick vector biology and for the prevention and treatment of tick-borne diseases, but often a challenge work even for a well trained expert. This grant proposal is to develop effective identification tools for the Dermacentor ticks, which intergrade molecular, morphological, host, ecological, geographic, and vector information together and can be used by scientists and professionals in the fields of vector biology and tick-borne diseases.